Generally, a duplexer is a device that performs the functions of separating and transmitting a transmitting frequency and a receiving frequency from several radio frequencies of a mobile communication device and selecting only required frequency from a lot of frequencies mixed with noise. The duplexer is connected with a lower side of an antenna of the mobile communication device so that the duplexer separates the transmitting and receiving frequencies, passes only required frequency during the transmission and the reception, and eliminates unnecessary frequencies. Recently, a high performance and small mobile communication device is a general tendency, and additionally, a multi-mode mobile communication device capable of performing a dual band type mobile communication device or a triple band type mobile communication device is rapidly developed. At the present time, as SAW duplexer is generally used according to the light and thin trend.
The SAW duplexer is proposed in U.S. Pat. No. 6,313,715 allowed to Andreas Bergmann et al.
FIG. 1 shows a schematic block diagram of the SAW duplexer disclosed in the U.S. Patent.
Referring FIG. 1, the SAW duplexer 10 includes a transmitting SAW filter 15, a receiving SAW filter 20, a transmitting capacitor 25, and an inductor 35. Though the capacitor 25 is connected to the transmitting SAW filter 15 in serial, the capacitor 25 can be connected to the receiving SAW 20 and the inductor 35 is generally connected to a signal line branched from an antenna 30.
The SAW duplexer 10 described above transmits a signal from a system to antenna 30 through the transmitting SAW filter 15 according to a frequency of the received signal, or performs a function for transmitting the received signal from the antenna 30 to the system through the receiving SAW filter 20.
The transmitting and receiving SAW filters 15 and 20 have a structure formed with single electrode or multiple electrodes on a substrate comprised of piezoelectric materials as disclosed in U.S. Pat. No. 6,297,580 allowed to Ryouichi Takayama et al, and these SAW filters 15 and 20 are widely used because of the smallness and lightness recently.
Presently, a code division multiple access (hereinafter referred to CDMA) terminal, a data card, and the like essentially have a duplexer for separating the transmitting and receiving signals from single antenna. A duplexer utilized in a mobile communication device of a frequency division duplexer (hereinafter referred to FDD) type like the CDMA type terminal includes a SAW band pass filter packaged with a high price ceramic package.
However, if the SAW band pass filter is utilized, the size of the duplexer is essentially increased, so that it is difficult to allocate all components on single chip and this fact becomes an obstacle for the high performance and miniaturization of the mobile communication device in future. For example, a personal communication service (PCS) terminal used in the present time uses a duplexer including two SAW filters having frequency bad about 1860 MHz to 1880 MHz and about 1880 MHz to 1910 MHz. Since, for this, a substrate with an area more than at least about 5×12 mm is required, it becomes an obstacle to miniaturize the mobile communication device.
Moreover, in case of the duplexer adopting the SAW filter, since the size of the chip is increased as well as the ceramic for package is high price, the manufacturing cost of the SAW duplexer is increased. In addition, since even an impedance matching network (IMN) needless of packaging with the ceramic package is packaged together the SAW filter, it is difficult to manufacture the SAW duplexer and the manufacturing cost thereof is increased.
In comparison with this, the FBAR filter can be manufactured in commercial quantity at low cost, and the size of the substrate in which the duplexer including the FBAR filter is formed can be reduced lower than about 3×3 mm. Moreover, since the FBAR filter can be used in a micro-frequency band and has advantages to be used in a PCS frequency band as well as a digital cellular system (DSC) frequency, the duplexer including the FBAR filter is researched and developed now. The FBAR is one to use a principle that if the piezoelectric material applies electrical energy to both electrodes disposed between, en electric field being timely varied within a piezoelectric layer is maintained and a bulk acoustic wave is generated according to the electric field.
FIG. 2 shows a schematic sectional view of a conventional FBAR filter.
By referring FIG. 2, the conventional FBAR filter has a structure of laminating a lower electrode layer 60, a piezoelectric layer 65, and an upper electrode layer 70 on a semiconductor board 55 in turn.
In to the FBAR filter 50, the piezoelectric layer 65 is laminated by sputtering a piezoelectric material such as zinc oxide (ZnO), aluminum nitride (AlN), and the like, then a device with s thin film structure for causing resonance according to the characteristics of the piezoelectric layer 65 is embodied into a filter.
U.S. Pat. No. 6,407,649 allowed to Pasi Tikka et al proposes a duplexer including an FBAR band pass filter.
FIG. 3 shows a sectional view of the duplexer including the FBAR band pass filter disclosed in the U.S. patent.
As shown in FIG. 3, the conventional FBAR duplexer 100 is comprised of a receiving filter 130 and a transmitting filter 135 on a substrate 105. The transmitting and receiving filters 130 and 135 have serial resonators 110 and 115 and shunt resonators 120 and 125, respectively. The serial resonators 110 and 115 and the shunt resonators 120 and 125 include a lower electrode 145, a piezoelectric layer 150, and an upper electrode 155, respectively, and are formed on a lower structure 140 including an inductor and a capacitor: respective shunt resonators 120 and 125 may be additionally formed with shunt tuners 160 on the upper electrode 155, and a transmitting tuning layer 165 may be formed on the upper electrode 155 of the serial resonator 115 and the shunt tuner 160 of the shunt resonator 125 of the transmitting filter 135, additionally.
However, according to the duplexer of the U.S. patent, since a duplexer module is manufactured by manufacturing the transmitting FBAR filter, the receiving FBAR filter, and the chip type inductor in the form of single device and packaging the same on the substrate, the size of the duplexer module is restricted to decrease. Moreover, since the transmitting and receiving FBAR filters, the inductor, the capacitor, and the like are manufactured separately and then integrated, the more time and higher cost for manufacturing the duplexer are required.